The combined steam and carbon dioxide reforming of methane (CSCRM) reaction was studied over a series of Ni-Mo-Sb catalysts to produce synthesis gas (H₂/CO). The catalysts modified with varying contents of antimony oxide (0-5 wt%) were prepared by the impregnation method. The catalytic reaction was conducted at 900 °C and 1 atm with a feed ratio of CH₄:CO₂:H₂O:Ar = 1:0.8:1.3:1 and WHSV = 40,000 h-1. The catalysts were characterized using N₂ Adsorption Desorption, X-ray diffraction (XRD), H₂-Temperature Programmed Reduction (H₂-TPR), Thermogravimetric analysis (TGA) and Transmission Electron Microscope (TEM). The highest catalytic activity and long-term stability were obtained over a Ni-Mo(1)-Sb(3)/Al₂O₃ catalyst and the superior catalytic behavior was closely related to the strong resistance to carbon formation.